For assessment of the hazard of “internal head injury” in head impact on a windshield, impact assessment methods according to C. W. Gadd (Gadd's hypothesis) and the Vienna Institute of Technology (Vienna hypothesis) are known. These methods are based on diametrically opposed concepts concerning the cerebral injury process. The respective assessment values of the two methods are Severity Index S and Tolerance Value J. Both methods relate assessment of an impact to the so-called Wayne State curve. The methods are examined as to their deviations from this curve and as to the comparability of results.It appears that Tolerance Value J, which makes use of an analogy to the biological injury process in assessment, compared to Severity Index S results in better reproducibility of the Wayne State curve, is not subject to limitations concerning time duration of impact and has thesimpler (linear) assessment measure. For comparison of assessment results, the values of Severity Index S must undergo correction.